Image range expansion control methods and apparatus

ABSTRACT

Image data is adjusted for display on a target display. Maximum safe expansions for one or more attributes of the image data are compared to maximum available expansions for the attributes. An amount of expansion is selected that does not exceed either of the maximum safe expansion and the maximum available expansion. Artifacts caused by over expansion may be reduced or avoided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/442,708 filed on Apr. 9, 2012, which claims the benefit of filingdate of U.S. Provisional Patent Application No. 61/473,691 filed on Apr.8, 2011, all of which are incorporated herein by reference in itsentirely.

TECHNICAL FIELD

The invention relates to displaying images and relates specifically tomethods and apparatus involving the adjustment of image data for displayon target displays.

BACKGROUND OF THE INVENTION

Display apparatus may employ any of a wide range of technologies. Somenon-limiting examples are plasma displays, liquid crystal displays(LCDs), cathode ray tube (CRT) displays, organic light emitting diode(OLED) displays, projection displays that use any of various lightsources in combination with various spatial light modulationtechnologies, and so on. Displays may be of a wide variety of types usedin any of a wide variety of applications. For example, the term displayencompasses without limitation apparatus such as: televisions, computerdisplays, media player displays, displays in hand-held devices, displaysused on control panels for equipment of different kinds, electronic gamedisplays, digital cinema displays, special purpose displays such asvirtual reality displays, advertising displays, stadium displays,medical imaging displays, and so on.

Different displays may have different capabilities in areas such as:black level, maximum brightness (display peak luminance), color gamut,and so on. The appearance of displayed images is also affected by theenvironment in which a display is being viewed. For example, theluminance of ambient lighting, the color of ambient lighting and screenreflections can all affect the appearance of displayed images.

With the increasing availability of high-performance displays (e.g.displays that have high peak luminance and/or broad color gamuts) comesthe problem of how to adjust images for optimum viewing on a particulardisplay or type of displays. Addressing this problem in simplistic wayscan result in noticeable artifacts in displayed images. For example,consider the case where an image that appears properly on a displayhaving a moderate peak luminance is displayed on a target display havinga very high peak luminance. If one expands the luminance range of theimage data to take advantage of the high peak luminance of the targetdisplay, the result may be poor due to objectionable artifacts that arerendered apparent by the range expansion. Artifacts may include, forexample, one or more of banding, quantization artifacts, visiblemacroblock edges, objectionable film grain and the like. On the otherhand, if the image is displayed on the target display without rangeexpansion, no benefit is gained from the high peak luminance that thetarget display can achieve.

There is a need for apparatus and methods for processing and/ordisplaying images that can exploit the capabilities of target displaysto provide enhanced viewing while reducing or avoiding undesirableartifacts.

SUMMARY OF THE INVENTION

This invention may be embodied in a wide variety of ways. These include,without limitation, displays (such as television, digital cinemadisplays, specialty displays such as advertising displays, gamingdisplays, virtual reality displays, vehicle simulator displays and thelike, displays on portable devices), image processing apparatus whichmay be integrated with a display, stand alone, or integrated with otherapparatus such as a media player or the like and media carryingnon-transitory instructions which, when executed by a data processorcause the data processor to execute a method according to the invention.

One non-limiting example aspect of the invention provides a method forimage processing. The method comprises obtaining image data and metadataassociated with the image data. The method processes the metadata withinformation characterizing a target display to determine a maximum safeexpansion for an attribute of the image data and a maximum availableexpansion for the attribute of the image data. The method processes theimage data to expand the attribute of the image data by the lesser ofthe maximum safe expansion and the maximum available expansion.

In some embodiments the attribute is dynamic range and processing theimage data comprises applying a tone mapping curve to the image data. Insome embodiments the attribute comprises a color gamut.

Another non-limiting example aspect of the invention provides imageprocessing apparatus. The image processing apparatus comprises a decoderconfigured to extract image data and metadata associated with the imagedata from a signal and a controller configured to process the metadatawith information characterizing a target display to determine a maximumsafe expansion for an attribute of the image data and a maximumavailable expansion for the attribute of the image data. The controlleris further configured to set an expansion amount equal to the smaller ofthe maximum safe expansion and the maximum available expansion. Theapparatus comprises an expander configured to expand the attribute ofthe image data by the expansion amount to yield modified image data.

Further aspects of the invention and features of specific embodiments ofthe invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting embodiments of theinvention.

FIG. 1 is a flow chart that illustrates a method according to an exampleembodiment of the invention.

FIG. 2 is a block diagram illustrating apparatus according to an exampleembodiment.

FIG. 2A is a flow chart illustrating a method that may be performed in acontroller in the apparatus of FIG. 2 or similar apparatus.

FIG. 3 is a block diagram illustrating apparatus according to analternative embodiment.

DESCRIPTION OF THE INVENTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive, sense.

FIG. 1 is a flow chart that illustrates a method 10 according to anexample embodiment of the invention. Method 10 may, for example, bepracticed at a target display or in an image processing device upstreamfrom a target display. Method 10 receives image data and adjusts theimage data for display on the target display. The adjustment comprisesexpanding one or more of dynamic range and color gamut.

Block 12 receives image data 14 comprising image content to be displayedon a particular target display. Block 12 may comprise, for example,receiving a data stream comprising the image data 14, accessing a fileor other data structure in a data store containing the image data 14, orthe like.

Block 15 receives metadata 16 associated with image data 14. Block 15may comprise, for example, extracting metadata 16 from a side stream,decoding metadata 16 that has been encoded in image data 14, obtainingmetadata 16 from a server or other repository by way of a datacommunication network, accessing a data structure containing metadata 16or the like. In some embodiments, metadata 16 and image data 14 are bothcontained in a common data container and blocks 12 and 15 respectivelycomprise extracting the image data 14 and associated metadata 16 fromthe data container.

Metadata 16 contains information that is indicative of a degree to whichimage data 14 can be expanded ‘safely’ in one or more respects. Here‘safely’ means without introducing visible artifacts that unacceptablydegrade image quality. One example of information that may be present asmetadata 16 is a direct indication of an acceptable degree of expansion(e.g. a number that directly indicates the degree to which the dynamicrange (e.g. luminance range) may be safely expanded). Another example isinformation specifying characteristics of a gamut of a source display onwhich the content of image data 14 was approved. The gamutcharacteristics may include one or more of: the colors of primaries ofthe source display, luminance range of the source display, black andwhite levels of the source display, points on a three-dimensional gamutboundary of the source display, or the like. Another example isinformation specifying encoding parameters for image data 14 such as bitdepth, encoding quality, color sub-sampling, and the like. Anotherexample of the makeup of metadata 16 is a combination of various ones ofthe information described above.

Block 18 determines from metadata 16 (or metadata 16 and image data 14in some embodiments) one or more maximum safe expansions that may beapplied to image data 14. For example, block 18 may determine a safedynamic range expansion and/or a safe chromaticity expansion.

Block 19 determines a maximum available expansion that may be applied toimage data 14 to fully exploit the capabilities of target display 30. Incases where method 10 is defined with knowledge of the capabilities oftarget display 30 (e.g. where method 10 is performed by a systemintegrated with target display 30) block 19 may determine the maximumavailable expansion based on metadata 16 (where the metadata 16specifies capabilities of the source display). For example, if thesource display has a peak luminance of 600 nits and target display 30has a peak luminance of 1800 nits then block 19 may determine that themaximum available expansion is expansion by a factor of 3 (by dividing1800 by 600 for example). In some cases the maximum safe expansion maybe less than the maximum available expansion. For example, in a casewhere the maximum safe expansion is 2 an expansion of 2 or less will beapplied. In the example case where an expansion of 2 is applied, theresulting peak luminance would be 1200 nits (2×600 nits), for thisexample.

As another example, block 19 may obtain information regarding one ormore capabilities of target display 30 by, for example, interrogatingtarget display 30 to determine its capabilities by way of an EDID,E-EDID, DisplayID or similar functionality, retrieving storedinformation regarding the characteristics of target display 30 from alocal data store or an accessible server or the like.

Block 20 compares the maximum safe expansion(s) from block 18 to themaximum available expansion(s) from block 19. If the maximum safeexpansion equals or exceeds the maximum available expansion then imagedata 14 may be expanded by the maximum available expansion for displayon the target display. If the maximum safe expansion is less than themaximum available expansion then the expansion of image data 14 shouldbe limited to the maximum safe expansion for display on the targetdisplay. Block 20 provides an expansion value equal to the lesser of themaximum safe expansion and the maximum available expansion for one ormore image characteristics that may be subjected to expansion.

Block 22 adjusts image data 14 for display on target display 30 byexpanding image data 14 according to the expansion value from block 20.In cases where the maximum safe expansion is less than the maximumavailable expansion, block 22 expands to an intermediate range that isbelow the maximum capabilities of target display 30. This avoids orkeeps to an acceptable level distortions and other artifacts particularto image data 14 that would have been introduced and/or raised tounacceptable levels by expansion exceeding the maximum safe expansionbut still within the capabilities of target display 30.

Some embodiments may provide an optional override control that a usermay operate to select an expansion exceeding a maximum safe expansion.For example, the override control may have the effect of causing amaximum safe expansion to be set to a very high value or the effect ofcausing the apparatus to ignore safe expansion limits. Operating thecontrol may have the effect of causing the maximum available expansionto be used. In another example, a user control may permit a user tomanually select an expansion. The selection may allow the user to causethe expansion to vary essentially continuously or may allow selectionfrom a set of discrete expansions. An indicator, display or otherfeedback device may warn the user when the selected expansion exceedsthe maximum safe expansion.

Advantageously, block 22 may expand some aspects of image data 14 by themaximum available expansion and other aspects by less than the maximumavailable expansion. For example, for a particular choice of image data14 and target display 30, chromaticity may be expanded by a maximumavailable expansion to take full advantage of an expanded color gamut oftarget display 30 while luminance is expanded by a maximum safeluminance expansion which is less than a maximum available luminanceexpansion.

In some example embodiments, block 22 performs expansion(s) according tosigmoidal expansion functions as described, for example, in U.S.application No. 61/453,107 filed on 15 Mar. 2011 and entitled METHODSAND APPARATUS FOR IMAGE DATA TRANSFORMATION which is hereby incorporatedherein by reference. That application describes image data expansionbased on parameterized sigmoidal tone curve functions. Block 22 mayperform expansion of image data 14 according to other suitable mappingsthat are constrained to limit the amount of expansion to not exceed themaximum safe expansion. For example, the target peak luminance used tocalculate the tone curve may be altered from a default value of themaximum capability of the target display, to a peak luminancecorresponding to the maximum safe range of expansion indicated bymetadata.

Block 24 stores and/or forwards the adjusted image data for display onthe target display. Block 26 displays the adjusted image data on thetarget display.

In some embodiments, image data 14 comprises video data. In suchembodiments, the maximum safe expansion may be different for differentportions of the video (e.g. for different scenes). Method 10 may beapplied separately for such different portions of the video.

Steps in the method of FIG. 1 may be executed by one or more programmeddata processors, by hardwired logic circuits, by configurable logiccircuits such as field programmable gate arrays (FPGAs) combinationsthereof and the like.

APPLICATION EXAMPLE

One application example is illustrated in FIG. 2. A television 50 has asignal input 52 connected to receive a signal containing video contentfor display from any of a tuner 53A, an external video signal input 53Band a data input 53C. Data input 53C may, for example, be connected tothe internet. The signal is delivered to a decoder 54 which includes ametadata reader 54A. Decoder 54 is connected to supply decoded videodata to an image processing system 55 comprising a dynamic range(luminance) expander 55A, a color gamut expander 55B and a controller55C configured to control dynamic range expander 55A and color gamutexpander 55B as described below. Image processing system may optionallyperform any of a wide variety of additional image processing functionsas are known in the art.

In operation, a signal is received at input 52. The signal is decoded toextract video data 57 and metadata 58. In one example, the metadataincludes the black point 58A, white point 58B and color gamut 58C of asource display (not shown) on which the video data was viewed forapproval and also a maximum dynamic range expansion 58D and a maximumcolor gamut expansion 58E.

Image processing controller 55C has access to or built into itselfinformation specifying the black point 59A, white point 59B and colorgamut 59C of display 50. Controller 55C may perform a method 60 as shownin FIG. 2A. Block 62 compares black point 59A and white point 59B oftarget display 50 to the black point 58A and white point 58B of thesource display. From this comparison, controller 55C determines whetherit should cause dynamic range expander 55A to: compress the dynamicrange of the video data (e.g. by applying a tone mapping curve toproduce altered video data having a lower dynamic range than video data57) or expand the dynamic range, or leave the dynamic range unaltered.Dynamic range expansion may be beneficial in cases where black point 59Aand white point 59B of target display 50 are more widely separated thanblack point 58A and white point 58B of the source display. Block 62 maycomprise taking a ratio (R_(TRG)/R_(SRC)) of the dynamic range of thetarget display R_(TRG) to the dynamic range of the source displayR_(SRC) and branching depending upon whether that ratio is greater than,equal to or less than one.

In the case that compression is called for (R_(TRG)/R_(SRC)<1) block 64configures dynamic range expander 55A to compress the video data fordisplay on television 50.

In the case that no compression or expansion is called for(R_(TRG)/R_(SRC)=1) block 65 configures dynamic range expander 55A to donothing or causes the video data to bypass dynamic range expander 55A.

In the case that expansion is called for (R_(TRG)/R_(SRC)>1) block 66picks the smaller of the ratio R_(TRG)/R_(SRC) and the maximum dynamicrange expansion 58D. Block 67 then configures dynamic range expander 55Ato expand the video data for display on television 50 by the amountdetermined by block 66 (or a smaller amount).

Consider the specific example where the comparison of the black andwhite points of the source and target displays indicates that the targetdisplay is capable of a dynamic range 1.5 times that of the sourcedisplay (e.g. R_(TRG)/R_(SRC)=1.5 thus a dynamic range expansion up to amaximum of 1.5 is possible). Suppose that metadata 58D indicates amaximum safe dynamic range expansion of 1.2. Then block 66 outputs 1.2because 1.2<1.5 and block 67 configures dynamic range expander 55A toexpand the dynamic range of the video data by a factor of 1.2.

In the illustrated embodiment, television 50 may perform either, both orneither of dynamic range expansion/compression and color gamutexpansion/compression. This is not mandatory. Television 50 could bemade to address dynamic range expansion/compression and not color gamutexpansion/compression or vice versa. Color gamut expansion orcompression may be handled in a similar manner to dynamic rangeexpansion or compression.

In the illustrated method 60, block 70 compares the color gamut 59C oftelevision 50 to the color gamut 58C of the source display. If the colorgamut 58C of the source display is larger than color gamut 59C oftelevision 50 then block 70 branches to block 72 which configures colorgamut expander 55B to compress (compression may include clipping,remapping etc.) the gamut of video data 57 to fit within color gamut59C.

If the color gamut 58C of the source display and the color gamut 59C oftelevision 50 are equal (to within a desired precision) then block 70branches to block 74 which leaves the color gamut of video data 72unaltered or causes color gamut expander 55B to be bypassed.

If the color gamut 58C of the source display lies within the color gamut59C of television 50 such that color gamut expansion is possible thenblock 70 branches to block 76 which determines a maximum amount of colorgamut expansion such that after color-gamut expansion the video datawill still be within the color gamut of television 50. Block 77 outputsthe smaller of the output of block 76 and the maximum safe color gamutexpansion 58E. Block 78 configures color gamut expander 55B to expandthe color gamut of video data 57 by the amount determined by block 77 ora smaller amount.

The image data is applied to display driver 80 which drives display 82to display images based on the adjusted image data.

FIG. 2 shows an optional safe expansion calculator stage 56. Safeexpansion calculator 56 is configured to calculate maximum safe dynamicrange expansion and/or maximum safe color gamut expansion based oninformation other than metadata 58D and 58E. For example, safe expansioncalculator 56 may calculate maximum safe dynamic range expansion 58D andmaximum safe color gamut expansion 58E in the case that metadataindicating these values is not present in metadata 58. Safe expansioncalculator may determine maximum safe dynamic range expansion frominformation such as: bit depth of the video signal; and/or encodingquality of the video signal. Metadata indicating values for theseparameters may be included in metadata 58. Safe expansion calculatormay, for example, comprise a lookup table which receives as inputs bitdepth and encoding quality of the video signal and produces a maximumsafe dynamic range expansion as an output. In some embodiments, safeexpansion calculator 56 is integrated with or associated with decoder54. In some embodiments, safe expansion calculator 56 is connected toreceive from decoder 54 information about a received video signal suchas bit depth of the video signal, encoding quality of the video signal,and/or other information useful for estimating a maximum safe expansionof the video signal.

FIG. 3 illustrates apparatus 50A according to an alternative embodimentin which a target display is separate from the apparatus that includesthe image processing system 55. FIG. 3 applies the same referencenumbers used in FIG. 2 for elements having the same or similarfunctions.

Apparatus 50A includes an interface 90 for data communication with aseparate target display 50B by way of a data communication path 91.Apparatus 50A also includes a user interface 94. Apparatus 50A isconfigured to obtain characteristics of target display 50B by way ofinterface 90 (for example by reading information from an EDID, E-EDID orDisplayID data structure hosted in target display 50B). In addition orin the alternative, apparatus 50A may receive information characterizingtarget display 50B by way of user interface 94. Data processed by imageprocessing system 55 is passed to target display 50B by way of a datacommunication path 96 that may be wired, wireless, electronic, opticalor the like. Data communication path 92 and data communication path 96may be separate or combined.

Apparatus, systems, modules and components described herein (includingwithout limitation inputs, tuners, decoders, readers, expanders,controllers, calculators, drivers, interfaces, and the like) maycomprise software, firmware, hardware, or any combination(s) ofsoftware, firmware, or hardware suitable for the purposes describedherein. Such software, firmware, hardware and combinations thereof mayreside on personal computers, set top boxes, media players, videoprojectors, servers, displays (such as televisions, computer monitors,and the like) and other devices suitable for the purposes describedherein. Furthermore, aspects of the system can be embodied in a specialpurpose computer or data processor that is specifically programmed,configured, or constructed to perform one or more of thecomputer-executable instructions explained in detail herein.

Image processing and processing steps as described above may beperformed in hardware, software or suitable combinations of hardware andsoftware. For example, such image processing may be performed by a dataprocessor (such as one or more microprocessors, graphics processors,digital signal processors or the like) executing software and/orfirmware instructions which cause the data processor to implementmethods as described herein. Such methods may also be performed by logiccircuits which may be hard configured or configurable (such as, forexample logic circuits provided by a field-programmable gate array“FPGA”). Image processing and processing steps as described above mayoperate on and/or produce image data (including without limitation videodata, tone mapping curves, metadata, and the like) embodied incomputer-readable signals carried on non-transitory media.

Certain implementations of the invention comprise computer processorswhich execute software instructions which cause the processors toperform a method of the invention. For example, one or more processorsin a display, personal computer, set top box, media player, videoprojector, server, or the like may implement methods as described hereinby executing software instructions in a program memory accessible to theprocessors.

Some aspects of the invention may also be provided in the form of aprogram product. The program product may comprise any non-transitorymedium which carries a set of computer-readable signals comprisinginstructions which, when executed by a data processor, cause the dataprocessor to execute a method of the invention. For example, such aprogram product may comprise instructions which cause a data processorin a display to adjust the image data for display on the display.Program products according to the invention may be in any of a widevariety of forms. The program product may comprise, for example, mediasuch as magnetic data storage media including floppy diskettes, harddisk drives, optical data storage media including CD ROMs, DVDs,electronic data storage media including ROMs, flash RAM, hardwired orpreprogrammed chips (e.g., EEPROM semiconductor chips), nanotechnologymemory, or the like. The computer-readable signals on the programproduct may optionally be compressed or encrypted. Computerinstructions, data structures, and other data used in the practice ofthe technology may be distributed over the Internet or over othernetworks (including wireless networks), on a propagated signal on apropagation medium (e.g., an electromagnetic wave(s), a sound wave,etc.) over a period of time, or they may be provided on any analog ordigital network (packet switched, circuit switched, or other scheme).

The teachings of the technology provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various examples described above can be combined to providefurther examples. Aspects of the system can be modified, if necessary,to employ the systems, functions, and concepts of the various referencesdescribed above to provide yet further examples of the technology.

Where a component (e.g. a software module, processor, assembly, device,circuit, input, tuner, decoder, reader, expander, controller,calculator, driver, interface, etc.) is referred to above, unlessotherwise indicated, reference to that component (including a referenceto a “means”) should be interpreted as including as equivalents of thatcomponent any component which performs the function of the describedcomponent (i.e., that is functionally equivalent), including componentswhich are not structurally equivalent to the disclosed structure whichperforms the function in the illustrated exemplary embodiments of theinvention.

These and other changes can be made to the system in light of the aboveDescription. While the above description describes certain examples ofthe system, and describes the best mode contemplated, no matter howdetailed the above appears in text, the system can be practiced in manyways. Details of the system and method for classifying and transferringinformation may vary considerably in its implementation details, whilestill being encompassed by the system disclosed herein. As noted above,particular terminology used when describing certain features or aspectsof the system should not be taken to imply that the terminology is beingredefined herein to be restricted to any specific characteristics,features, or aspects of the system with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the system to the specific examples disclosedin the specification, unless the above Description section explicitlyand restrictively defines such terms. Accordingly, the actual scope ofthe system encompasses not only the disclosed examples, but also allequivalent ways of practicing or implementing the technology under theclaims.

From the foregoing, it will be appreciated that specific examples ofsystems and methods have been described herein for purposes ofillustration, but that various modifications, alterations, additions andpermutations may be made without deviating from the spirit and scope ofthe invention. The embodiments described herein are only examples. Thoseskilled in the art will appreciate that certain features of embodimentsdescribed herein may be used in combination with features of otherembodiments described herein, and that embodiments described herein maybe practised or implemented without all of the features ascribed to themherein. Such variations on described embodiments that would be apparentto the skilled addressee, including variations comprising mixing andmatching of features from different embodiments, are within the scope ofthis invention.

As will be apparent to those skilled in the art in the light of theforegoing disclosure, many alterations and modifications are possible inthe practice of this invention without departing from the spirit orscope thereof. Accordingly, the scope of the invention is to beconstrued in accordance with the substance defined by the followingclaims.

What is claimed is:
 1. A method for image processing, the methodcomprising: storing in a non-transitory memory a data stream receivedover a digital network; obtaining, from the stored data stream, imagedata comprising a digital image to be displayed and metadata, whereinthe metadata from the data stream includes both: (i) a multiplicativefactor value for safe luminance dynamic range expansion for a scene ofthe image data; and (ii) metadata indicative of a luminance dynamicrange of a source display, the metadata including parameters for each ofcolor primaries, black level, and white level of the source display;obtaining target display information to determine a luminance dynamicrange of the target display; computing, by one or more processors, amaximum available expansion of a luminance dynamic range for the imagedata as a ratio of the luminance dynamic range of the target display andthe luminance dynamic range of the source display; comparing thecomputed maximum available expansion and the factor value obtained fromthe data stream; and by the one or more processors, expanding theluminance dynamic range of the image data by the lesser of the factorvalue obtained from the data stream and the computed maximum availableexpansion.
 2. The method of claim 1 wherein obtaining target displayinformation includes interrogating the target display.
 3. The method ofclaim 2 further comprising displaying the image data with expandedluminance dynamic range by the target display.
 4. The method of claim 1further comprising displaying by the target display the image data withexpanded luminance dynamic range.
 5. A method for image processing, themethod comprising: storing in a non-transitory memory a data streamreceived over a digital network; obtaining, from the stored data stream,image data comprising a digital image to be displayed and metadata,wherein the metadata from the data stream includes both: (i) amultiplicative factor value for safe luminance dynamic range expansionfor a scene of the image data and (ii) metadata indicative of aluminance dynamic range of a source display, the metadata includingparameters for each of color primaries, black level, and white level ofthe source display; obtaining target display information to determine aluminance dynamic range of the target display; computing, by one or moreprocessors, a maximum available expansion of a luminance dynamic rangefor the image data as a ratio of the luminance dynamic range of thetarget display and the luminance dynamic range of the source display;comparing the computed maximum available expansion and the factor valueobtained from the data stream; and by the one or more processors,expanding without override control the luminance dynamic range of theimage data by the lesser of the factor value obtained from the datastream and the computed maximum available expansion using a sigmoidalexpansion function, and by the one or more processors, expanding withoverride control the luminance dynamic range of the image data by thecomputed maximum available expansion.
 6. A method for image processing,the method comprising: storing in a non-transitory memory a data streamreceived over a digital network; obtaining, from the stored data stream,image data comprising a digital image to be displayed and metadata,wherein the metadata from the data stream includes both: (i) amultiplicative factor value for safe luminance dynamic range compressionfor a scene of the image data and (ii) metadata indicative of aluminance dynamic range of a source display, the metadata includingparameter for each of color primaries, black level, and white level ofthe source display; obtaining target display information to determine aluminance dynamic range of the target display; computing, by one or moreprocessors, a maximum available compression of a luminance dynamic rangefor the image data as a ratio of the luminance dynamic range of thetarget display and the luminance dynamic range of the source display;comparing the computed maximum available compression and the factorvalue obtained from the data stream; and by the one or more processors,compressing without override control the luminance dynamic range of theimage data by the lesser of the factor value obtained from the datastream and the computed maximum available compression using a sigmoidalfunction, and by the one or more processors, compressing with overridecontrol the luminance dynamic range of the image data by the computedmaximum available compression.
 7. A non-transitory computer-readablemedium storing a sequence of instructions, which when executed by one ormore computing processors, causes the one or more computing processorsto perform the method of claim
 1. 8. A non-transitory computer-readablemedium storing a sequence of instructions, which when executed by one ormore computing processors, causes the one or more computing processorsto perform the method of claim
 2. 9. A non-transitory computer-readablemedium storing a sequence of instructions, which when executed by one ormore computing processors, causes the one or more computing processorsto perform the method of claim
 3. 10. A non-transitory computer-readablemedium storing a sequence of instructions, which when executed by one ormore computing processors, causes the one or more computing processorsto perform the method of claim
 4. 11. A non-transitory computer-readablemedium storing a sequence of instructions, which when executed by one ormore computing processors, causes the one or more computing processorsto perform the method of claim
 5. 12. A non-transitory computer-readablemedium storing a sequence of instructions, which when executed by one ormore computing processors, causes the one or more computing processorsto perform the method of claim
 6. 13. An apparatus comprising one ormore computing processors configured to perform the method of claim 1.14. An apparatus comprising one or more computing processors configuredto perform the method of claim
 2. 15. An apparatus comprising one ormore computing processors configured to perform the method of claim 3.16. An apparatus comprising one or more computing processors configuredto perform the method of claim
 4. 17. An apparatus comprising one ormore computing processors configured to perform the method of claim 5.18. An apparatus comprising one or more computing processors configuredto perform the method of claim 6.